Definition
Joinder of parties is the procedural mechanism by which two or more persons are brought together as parties on the same side or opposing sides of a single lawsuit. It encompasses both the joining of multiple plaintiffs (co-plaintiffs) and multiple defendants (co-defendants) in one action.
Joinder serves efficiency goals: a single proceeding can resolve claims arising from the same transaction or occurrence rather than forcing duplicative litigation. Modern procedural systems distinguish between two categories of party joinder based on whether participation is optional or required:
1. PERMISSIVE JOINDER: Parties may join or be joined when their claims or the claims against them arise from the same transaction or occurrence and share at least one common question of law or fact. No party is compelled; the court has discretion to sever if joinder creates prejudice or unmanageable complexity.
2. COMPULSORY JOINDER (also called necessary and indispensable parties): Certain parties must be joined if their absence would prevent complete relief, would impair their ability to protect their own interests, or would expose existing parties to inconsistent obligations. If a required party cannot be joined (due to jurisdictional limits, for example), the court must decide whether the action can proceed without them or must be dismissed entirely.
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Common Confusion
JOINDER OF PARTIES vs. JOINDER OF CLAIMS: These are related but distinct concepts. Joinder of parties concerns who is in the lawsuit; joinder of claims concerns how many and what types of legal theories a party may assert within a single action. A researcher finding references to "joinder" in historical sources must determine which type is meant — early treatises and cases often used the unqualified word to cover both.
NECESSARY vs. INDISPENSABLE PARTIES: Under the Federal Rules of Civil Procedure as revised in 1966, the older terminology of "necessary" and "indispensable" parties was deliberately replaced with a more flexible, factor-based inquiry. Historical sources use these terms freely and in ways that do not map cleanly onto modern doctrine. An "indispensable" party in a pre-1966 case may have had very different procedural consequences than the same characterization today.
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Core Elements
For permissive joinder of plaintiffs or defendants under modern federal practice, two conditions must be met:
1. The claims asserted arise out of the same transaction, occurrence, or series of transactions or occurrences.
2. Any question of law or fact common to all parties will arise in the action.
For compulsory joinder, courts apply a multi-factor analysis asking whether:
1. Complete relief can be accorded among existing parties without the absent person.
2. The absent person's interests may be impaired or impeded by the action proceeding without them.
3. Existing parties risk inconsistent obligations if the absent person is not joined.
4. If joinder is required but not feasible, whether equity and good conscience permit the action to proceed anyway — considering prejudice, adequacy of judgment, and the plaintiff's access to an alternative forum.
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Why It Matters in Research
The vocabulary problem is significant. Pre-1938 federal practice (before the Federal Rules of Civil Procedure) governed joinder through a patchwork of equity rules, common law forms, and the Field Code in many states. A researcher reading a 19th-century case about party joinder is operating in a world where distinctions between law and equity shaped who could be joined and how. The same conduct that would produce a single consolidated proceeding under modern rules might have required separate suits at law and in equity.
The 1966 amendments to FRCP Rule 19 are a hard break in the research timeline. Any case, treatise, or secondary source discussing "indispensable parties" before 1966 may use doctrine that modern courts expressly rejected. Black's Law Dictionary editions predating the 1966 amendments carry forward the older framework without flagging that it was superseded.
State practice varies considerably. Many states have adopted rules substantially similar to the Federal Rules, but some retain older joinder requirements or use different threshold standards for compulsory joinder. Research in state court records should not assume federal doctrine applies.
Class actions represent an extension of joinder logic to situations where individual joinder is impractical — a researcher tracing the intellectual lineage of class certification will pass through joinder doctrine. Interpleader, intervention, and impleader are all procedural cousins that appear in the same corpus clusters as joinder materials.
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Historical Dictionary Support
Black's Law Dictionary defines joinder of parties concisely as "the uniting of two or more persons as co-plaintiffs or as co-defendants in one suit." This definition accurately captures the core of the concept but offers no procedural framework — it does not distinguish permissive from compulsory joinder, nor does it signal the equity/law divide that dominated historical practice.
Older editions of Black's are consistent across printings on the surface definition but do use the necessary/indispensable distinction that modern practice has moved away from. Researchers relying on Black's alone will not be alerted to the 1966 doctrinal shift.
What historical dictionaries uniformly miss is the jurisdictional dimension: whether a party's joinder is feasible at all is often a function of personal jurisdiction, subject matter jurisdiction, and in federal court, the impact of adding a non-diverse party on diversity jurisdiction. This remains a live research problem invisible in dictionary definitions.
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Jurisdictional Note
Federal courts apply FRCP Rules 19 and 20, which many states have substantially adopted. However, some states — particularly those with codes predating or diverging from the Federal Rules — apply different tests for required joinder or place different emphasis on prejudice factors. Equity-based joinder doctrine survives in some state court practice more robustly than in federal courts.
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Encyclopedia Cross-Reference
The Law Mind Contracts & Commercial Law Encyclopedia: Novation — Substitution of Parties (contracts_106). Relevant when researching joinder in the context of contract disputes where a party has been substituted, released, or added by agreement.
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